Acanthamoeba has been shown to secrete lysosomal enzymes into the culture medium. This release of lysosomal enzymes was energy-dependent and was not due to cell lysis. The five hydrolases studied showed three patterns of secretion: (a) secretion of acid phosphatase and Beta-glucosidase was stimulated by phagocytosis of nutrient particles, but anaffacted by phagocytosis of indigestible particles; (b) secretion of N-Acetyl-Beta-hexosaminidase and esterase was unaffected by phagocytosis of nutrient particles and was inhibited by phagocytosis of latex beads; (c) secretion of Alpha-galactosidase was stimulated by phagocytosis of bouth nutrient and indigestible particles. These results are interpreted to be evidence for subpopulations of lysosomes that fuse variably with phagosomes and/or plasma membranes.